Primary amines are used as versatile intermediates, for example, for preparing pharmaceuticals or agrochemicals (Amines, Aliphatic, Ullmann's Encyclopedia of Industrial Chemistry, 2012, Vol. 2, pp. 647-695). Enantiomerically pure, chiral amines in particular are valuable building blocks in this connection.
Primary amines may be prepared in various ways, although the reductive amination of carbonyl compounds with ammonia and hydrogen is a particularly atom-efficient method, since no further co-products arise apart from water.

On an industrial scale, heterogeneous catalysts are mostly used for this purpose, although with these systems, however, enantiomerically pure chiral amines cannot be obtained. Commercially, primary, enantiomerically pure chiral amines are usually prepared from the racemic mixtures of the corresponding amines via multistage enzymatic methods (D. Ghislieri, N. J. Turner, Top. Catal. 2014, 57, 284-300; Angew. Chem. Int. Ed. 2004, 43, 788-824).
A direct method for preparing primary amines is homogeneously catalyzed reductive amination, which may also be conducted asymmetrically for the synthesis of enantiomerically pure chiral amines (Thomas C. Nugent (Ed.), Chiral Amine Synthesis, 2010, pp. 225-245, Wiley-VCH, Weinheim).
U.S. Pat. No. 6,884,887 discloses the reductive amination of carbonyl compounds with amines and hydrogen using homogeneously dissolved transition metal phosphane complexes. When using ammonia for preparing primary amines using the rhodium and iridium catalysts described, which bear bidentate phosphane ligands, unsatisfactory selectivities at high rates of conversion are obtained under these conditions, however, due to the undesired hydrogenation of the carbonyl compound to the corresponding alcohol. The highest amine:alcohol selectivities described here, in the case of complete conversion of the carbonyl compound, are 4:1, i.e. 20% of the undesired alcohol is formed as by-product in the system described. For the amination with NH3 in this case, no catalysts bearing a carbonyl ligand were used and no acid as co-catalyst was added. The asymmetric amination with ammonia with the catalysts claimed is also not substantiated by examples. A disadvantage of this system is the formation of relatively large amounts of alcohols as undesired by-products.
US2004/0267051 discloses the reductive amination of carbonyl compounds with amines using homogeneously dissolved transition metal phosphane complexes, in which not hydrogen but hydrogen donors such as ammonium formate from a transfer hydrogenation are used. According to US2004/0267051, a distinctly higher selectivity is achieved with respect to the amine (no formation of alcohol at conversions of up to 96% of the carbonyl compound) by transfer hydrogenation using comparable transition metal catalysts, as described in U.S. Pat. No. 6,687,887, than by using hydrogen as reducing agent. According to US2004/0267051, the amines may also additionally be prepared enantioselectively using chiral phosphane ligands. A disadvantage of this method is that very inexpensive hydrogen cannot be used as reducing agent in order to achieve high selectivities but significantly more expensive reducing agents have to be used for a transfer hydrogenation.
It is likewise proposed in Chem. Eur. J. 2014, 20, 245-252 that the reductive amination of ketones to primary amines is carried out using ammonium formate as reducing agent and NH3 source in order to achieve the highest possible selectivities of the desired amine and to suppress the formation of alcohols. In this case, homogeneously dissolved half-sandwich iridium complexes are used as catalysts. Similarly disadvantageous is that inexpensive hydrogen cannot be used as reducing agent and in addition formamides of the products are also formed as by-products, which are only converted to the desired amine by a downstream hydrolysis.
The object, therefore, consisted of providing a method by which the disadvantages discussed above can be avoided. Such a method should be simple to carry out, be carried out using ammonia as amine source and hydrogen as reducing agent and afford as little as possible of the undesired alcohols as by-product. In addition, it should also be possible using this method to prepare the amines enantioselectively.